1. Field of the Invention
The present invention relates to a biodegradable plastics and biodegradable plastic products thereof and particularly, it relates to a biodegradable aliphatic polyester composition and flexible moldings, which are prepared by blending aliphatic polyester containing polylactic acid as its major constituent with a plasticizer having a specific structure.
2. Description of the Prior Art
Plastic products of polyethylene, polystyrene, polypropylene, polyvinyl chloride and the like have been utilized in various and wide fields of food packaging, building materials, home electrical appliances and the like and have become indispensable in daily life.
However, while on one hand such plastic products have a feature of durability, they also have disadvantages in causing destruction to the environment, such that when they have fulfilled their utilizing purpose and have become waste, they show poor degradability in nature because of their superior durability and affect the biological system.
For overcoming such disadvantages of plastics, biodegradable plastics have received considerable attention. Biodegradable plastics are degraded into low molecular weight compounds in an extremely short time by enzymatic actions produced by microorganisms which inhabit the environment, and is finally degraded into inorganic substances such as water and carbon dioxide.
With the growing awareness of environmental problems in recent years, recycling of plastic products has been legislated, and along with recycling and reuse thereof, the so-called biodegradable plastics, which can be easily degraded in the environment, have received considerable attention and both governments and the private sector have keenly carried out research and development thereof. As uses thereof, application to agricultural materials (such as, for example, sheets or films to be used for greenhouses for growing root vegetables) to be used in the environment, materials (such as, for example, food package films, sheets, or bags) to be used in the food packaging field where collection is difficult and, other packaging materials (such as, for example, sheets, films, or bags for packaging clothes or convenience goods), etc., has been anticipated.
Such biodegradable plastics can be divided into some large groups such as microorganism-producing system, natural substance-utilizing system, and chemically synthesized system, and wherein aliphatic polyester system, denatured polyvinyl alcohol system, denatured starch system, and other system are now on first steps for practical use.
Polybutylene succinate, polyhydroxybutyrate and the like can be used as for aliphatic polyester plastics, and polylactic acid can be used as for a semi-synthetic copolymer.
Polylactic acid is a crystalline thermoplastic macromolecular having tensile strength equivalent to that of polyethylene and transparency equivalent to that of polyethylene terephthalate, is used in medical suture threads and the like, is highly safe and, when burned, the small combustion calorie which is approximately ⅓ of that of polyethylene, polypropylene or the like causes less damage to an incinerator, and generates no poisonous gas. Moreover, with these advantages, in recent years, research and development of manufacturing methods, application, uses and the like have become active, therefore, diversification of uses and an accompanying increase in production are expected in the future.
Polylactic acid has such advantages, however, on the other hand, wherein plastic products thereof are hard and the utilization has been restricted in fields which require softness and, particularly, in films, package materials and the like. The addition of a plasticizer is one of method for improving hardness and providing softness, and for actions as a plasticizer, conditions such as:
(1) being excellent in compatibility with a polymer or a resin to be plasticized,
(2) having good plasticizing efficiency, and
(3) showing no deterioration in performance due to volatilization, transition, or oozing after processing, must be provided.
As a plasticizer for containing polylactic acid and a resin containing polylactic acid as its major constituent, triacetin (Shimazu Hyoron, Vol.54, No. 155 (1997. 3): Japanese Unexamined Patent Publication No. Hei-6-184147: Japanese Unexamined Patent Publication No. Hei-7-177826), ester of aliphatic dicarboxylic acid and/or chain molecular diol or an aliphatic polyester containing these as its major constituents (Japanese Unexamined Patent Publication No. Hei-8-199053: Japanese Unexamined Patent Publication No. Hei-8-245866), triacetin, tributyn, or butylphthalyl butylglycolate (Japanese Unexamined Patent Publication No. Hei-9-296103), a glycerol derivative including an alkyl group having carbon numbers 1-10 (Japanese Unexamined Patent Publication No. Hei-11-323113), diacetyl monoacyl glycerol inclduing an acyl group having carbon numbers 6-18 (Japanese Unexamined Patent Publication No. 2000-302956) and the like have been disclosed. However, each of these has advantages and disadvantages in performance and physical characteristics and is not sufficiently satisfactory.
The Objects of the Invention:
It is an object of the present invention to provide a plasticizer for providing aliphatic polyester, in particular, polyactic acid with flexibility, an aliphatic polyester composition using the same and flexible moldings which are obtained by molding said composition into films, sheets, bags and the like.
In order to solve the above problem, the present inventors have repeatedly carried out intensive research studies and consequently discovered that the above object is achieved by blending aliphatic polyester with a specific compound as a plasticizer. Based on this knowledge, the present invention has been reached.
In order to solve the above problem, the present invention has the following constructions.
1. An aliphatic polyester composition which contains, with respect to 100 parts by weight of aliphatic polyester, polyglycerol acetic ester by 5-50 parts by weight.
2. An aliphatic polyester composition which contains, with respect to 100 parts by weight of aliphatic polyester, polyglycerol acetic ester and a compound represented by the following general formula (1) by 5-50 parts by weight. 
In the formula, one or two of R1, R2, and R3 is an acyl group having carbon numbers 8-22 and the rest thereof are acetyl groups or hydrogen atoms.
3. An aliphatic polyester composition as set forth in claim 2, wherein
in the general formula (1), one or two of R1, R2, and R3 is an acyl group having carbon numbers 8-18 and the rest thereof are acetyl groups.
4. An aliphatic polyester composition as set forth in the above 2, wherein
the compound represented by the general formula (1) is at least one selected from glycerol diacetomonocaprirate, glycerol diacetomonolaurate, and glycerol diacetomonooleate.
5. An aliphatic polyester composition as set forth in any of the above 1-4, wherein
the polymerization degree of polyglycerol as a component of polyglycerol acetic ester is 2-4.
6. An aliphatic polyester composition as set forth in any of the above 1-5, wherein
the acetylization degree of polyglycerol acetic ester is 50-100%.
7. An aliphatic polyester composition as set forth in any of the above 1-6, wherein
the polyglycerol acetic ester is at least one or a mixture of two or more selected from diglycerol diacetate, diglycerol triacetate, and diglycerol tetraacetate.
8. An aliphatic polyester composition in which the aliphatic polyester as set forth in any of the above 1-7 is polylactic acid.
9. Flexible products which are obtained by molding the aliphatic polyester composition as set forth in any of the above 1-8 into films, sheets, bags or the like.